From defe12df51249200214b7781ebe23345df474655 Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Tue, 24 Jan 2012 04:44:01 +0000
Subject: [PATCH] Preserve <def,undef> flags in CoalesceExtSubRegs.

This won't have an effect until EliminateRegSequences() starts setting
the undef flags.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148779 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/TwoAddressInstructionPass.cpp | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/lib/CodeGen/TwoAddressInstructionPass.cpp b/lib/CodeGen/TwoAddressInstructionPass.cpp
index dc6b3420ab1..8002ff2c64e 100644
--- a/lib/CodeGen/TwoAddressInstructionPass.cpp
+++ b/lib/CodeGen/TwoAddressInstructionPass.cpp
@@ -1728,8 +1728,10 @@ TwoAddressInstructionPass::CoalesceExtSubRegs(SmallVector<unsigned,4> &Srcs,
         CanCoalesce = false;
         break;
       }
-      // Keep track of one of the uses.
-      SomeMI = UseMI;
+      // Keep track of one of the uses.  Preferably the first one which has a
+      // <def,undef> flag.
+      if (!SomeMI || UseMI->getOperand(0).isUndef())
+        SomeMI = UseMI;
     }
     if (!CanCoalesce)
       continue;
@@ -1738,7 +1740,9 @@ TwoAddressInstructionPass::CoalesceExtSubRegs(SmallVector<unsigned,4> &Srcs,
     MachineInstr *CopyMI = BuildMI(*SomeMI->getParent(), SomeMI,
                                    SomeMI->getDebugLoc(),
                                    TII->get(TargetOpcode::COPY))
-      .addReg(DstReg, RegState::Define, NewDstSubIdx)
+      .addReg(DstReg, RegState::Define |
+                      getUndefRegState(SomeMI->getOperand(0).isUndef()),
+              NewDstSubIdx)
       .addReg(SrcReg, 0, NewSrcSubIdx);
 
     // Remove all the old extract instructions.